When cutting out non-traditionally shaped ATCs by hand, you might end up with uneven edges. Also, when you glue them together they might not match perfectly. I use sandpaper to even things up and to make minor adjustments. In addition to the sandpaper, I use a filing tool set made by Basic Grey. It comes with 5 different files that make it easy to get into small spaces. The set is available at many online stores.
Precision File Set by Basic Grey